1. Field of the Invention.
The present invention relates to housings for pressure sensing cells and associated signal conditioning and transmitter circuitry.
2. Description of the Prior Art.
Conventional differential pressure transducers incorporate a sensor cell that has flanges that permit connecting the sensor to two separate sources of pressure, and generally are used for clamping the sensor. For example, flanges for clamping a sensing cell are shown in U.S. Pat. No. 4,466,290. This patent also shows a system for attaching a manifold in position. In such a device as shown in this patent, and also in U.S. Pat. No. 3,618,390, the flanges are used for clamping the sensing cell, and a separate housing is utilized for the signal conditioning circuitry, preferrably a two wire transmitter circuit. The separate housing increases cost, and while it isolates the circuitry from the sensing cell mounting, in many applications where low cost transmitters are desirable, and where the specifications for operation are not as critical as others, it is desirable to minimize the number of parts, and yet provide all of the functions of existing transmitters.
Bourns Instruments, Inc. of Riverside, California also sells differential pressure transmitters. Their Models 8100 and 8400 show transmitters having separate circuit or convertor circuitry housings as well as flanges for connection to the pressure sources.
Bourns Instruments, Inc. Model 5020 solid state differential pressure transmitter also shows a housing that has end flanges fastened to a body with cap screws, but in this instance the circuitry used with the unit is housed in a separate portion of the housing extending laterally from the main part of the housing.
The CEC Division of Bell and Howell makes a pressure transducer type 4-351 which utilizes a strain gage type sensor inside a housing having flanges at its ends, and circuitry within the housing. In such a unit, however, it is not necessary to provide clamping to the sensor, and thus the end members for the housing are merely fastened onto the center section with cap screws. This is a small solid state unit, using a strain gage sensing cell.